PROBLEM SOLVED. -- at least for me
With my newly purchased ODB cable I ran VCDS to check fault codes on my TDI and found an intermittent cam sensor fault, which was one of the suspected reasons for the starting problems with a warm engine. I changed the cam sensor and the problem has now disappeared.
I now have a theory what happened in my car :
Often after a short stop for shopping I had to crank the engine for two to four 5 sec periods before it started because of my broken cam sensor. This resulted in vapor bubbles in the fuel return pipe that normally would be no problems as the the return pipe goes to the fuel tank. But in this case the fuel pre heating valve placed at the fuel filter has not open yet and the return fuel with it’s bubbles is directed into the filter and creates a lock in the fuel supply. Then after driving for a minute or two the air lock in the fuel supply reaches the engine and result in a stop. After a number of cranks the engine can be started again and the hole thing repeats again if the preheating valve is not opened .
The preheating valve is opened when the temperature is reaching 30°C and directs the return fuel to the tank which ends the terminates the faulty behavior.
After changing the cam sensor I have no problems starting the car and the problem with air in the fuel pipe is avoided
/Freddie